U.S. Pat. No. 2,558,854 describes how chocolate is obtained from cocoa pods, that is the fruit of Theobroma cacoa.
First quality chocolate does not have an off-flavour which has been described by various terms including mouldy, musty or earthy. Chocolate makers therefore cannot use, in the manufacture of top quality chocolate, any beans which might be responsible for such a flavour. They therefore specify only top quality beans.
Specifically, the consensus is that bean feedstocks with a mouldy bean content of anything more than 3% is unacceptable. The bean mould may be internal, external, or both. However, research work published in 1987 (Baigrie et al, Flavour Science and Technology, 1987, pp 133-141) indicates that many feedstocks with a high level of mould nevertheless do not produce chocolate with a mouldy flavour. Thus, it remains unclear which beans are suitable for making top quality chocolate, and which are not.
In his 1987 paper, Baigrie identified 2-methoxy-3-isopropylpyrazine, MIPP, as being the major contributor for the off-flavour, termed mouldy/musty or earthy/musty by flavourists. He further asserts that the off-flavor in poor quality cocoa beans may in fact have nothing to do with the actual presence or absence of mould in or on the beans.
Baigrie found that MIPP supresses chocolate flavour but that this effect was not confined to MIPP and that the flavour suppression mechanisms "are clearly complex".
That off flavours in cocoa beans can be removed by superheated steam is already known. See, for example, U.S. Pat. No. 4,861,615 in which a screw extruder receives raw cocoa bean fragments which are subject then to the action of high pressure steam before being mixed, kneaded and de-gassed. Roasting is effected in a third zone of the extruder by heat delivered through the extruder housing wall.
U.S. Pat. No. 2,278,483 (published Apr. 7, 1942) teaches that shells of cocoa beans can be loosened by subjecting the shells to the action of steam at substantial superheat and elevated pressure. As high a pressure as is practicable is advocated, with a sudden release of this pressure which has an explosive effect on the beans, for better separation of nibs from shells. An effect on flavour development is noted, if the treatment is continued longer than required for deshelling, but it is explained that this flavour development is achieved anyway, during the subsequent processing of the nibs. The reader is urged to select the highest feasible pressure, in order for the treatment time to be as short as possible, for economic reasons. Treatment times of from 5 to 50 seconds and from 5 to 120 seconds, are specified.
DD 98817 discloses adding water to cocoa mass and then heating the mass, in order that the consequent water evaporation improves the flavour of the cocoa assisting the efflux of flavour-spoiling constituents.
SU-A-1324626 discloses an apparatus for hydro-thermal treatment of cocoa beans, but the document is silent as to any details of the process conditions.
EP-A-0061229 discloses processing a wide range of materials including cereal grains and cocoa beans with heat and pressure. It is noted that it is customary to improve the organoleptic (taste, appearance, odour) characteristics of cereals by such techniques. Temperatures of at least 200.degree. C. are advocated, together with high pressures, preferably in a range of 5-35 atmospheres, for periods of time such as 3-13 seconds. The treatment killed more than 99.9% of bacteria in two samples of cocoa beans.
EP-A-0068221 proposes treating cocoa beans in their shells by first dampening and then heat treatment at temperatures of at least 150.degree. C. This facilitates subsequent separation of nibs from shells, and kills bacteria in the feedstock. The nibs are then roasted.
U.S. Pat. No. 4,970,090 discloses processes for improving and strengthening the flavour of water or ethanol cocoa extract by holding it at elevated temperature, greater than 125.degree. C. but less than 150.degree. C., for periods of time of from 3.5 to 4.5 hours.
The state of the art contains many disclosures of the use of steam in processes to reduce the bacterial content of raw cocoa beans. DE-A-3902679 provides a survey of the art and itself suggests the use of saturated steam at 0.6 Mpa (6 bar) and 160.degree. C. for this purpose.